Continuous cellulose nitration



Aug- 18, 1953 w. c. RAMSEY 2,649,441

CONTINUOUS CELLULOSE NITRATION Filed April 14, 1950 V INVENTORZ WILLIAM C. RAMSEY vi I ATTORNEYS.

3 exerted to draw the strip 3 through the tube about roller 7 thus tends to straighten the reaches of strip between roller 1 and the opposite ends of the tube, and at the same time flattens the lateral bow in the strip.

At the exit end of the nitrating tube, i. e., at the end of leg remote from header 6, a pair of squeeze rolls 8 are provided, one above and one below the strip 3. The squeeze rolls 8 are positively driven from any suitable source of power, and their rate of rotation will determine the lineal velocity of the strip 3 in passing through the nitrating tube. The squeeze rolls 8 are also radially adjusted so as to wring the nitrated strip substantially free of acid.

Fresh nitrating acid is charged into tube 5 at inlet 9, so that the tube is filled to the level indicated at [0, and the spent acid is discharged through outlet ll adjacent the cellulose intake end of leg 4.

A drain l2 may be provided at the junction header 6 for draining the acid from the tube whenever necessary.

In order to control the temperature of the nitration, the tube, consisting of legs 4 and 5, may be provided with any suitable heating device, such, for example, as an electrical resistance coil, or steam coils I3, [4, I5, and I6. It is preferable to divide the heating coils into separately controllable sections, in order thereby to vary the temperature lengthwise of the legs 4 and 5. Suitable temperature-indicating or automatic temperature-regulating devices may be provided along the length of the tube, as indicated a I1, [8, l9 and 20.

The cellulose material supplied is in the form of paper, made from any suitable pulp, and, depending upon the end use of the nitrated cellulose, may be more or less pure. For the manufacture of smokeless powder, it is most desirable that the paper be as free as possible of substances other than cellulose.

The nitrating acid may be the usual mixture of nitric acid and dehydrator, such as sulphuric, phosphoric, or acetic acids. Depending upon the extent of nitration desired, the content of nitric acid in the nitrating acid mixture may vary from about 75 per cent to about 50 per cent, and the time period within which a given increment of cellulose remains immersed in the nitrating bath may vary from about minutes to about 120 minutes. The temperature maintained within the nitrator may be varied between about 25 C. and about 65 C.

In a typical case, to produce nitrocellulose having a degree of nitration within the guncotton range, for example, 13.45 per cent, the fresh nitrating acid may be composed as follows:

I Percent Nitric acid 73.5 Phosphoric acid (HaPOa) 25.8 Water 0.7

Percent Nitric acid 63.5 Phosphoric acid 30.5

Water 6.0

Stability tests conducted upon the nitrocellulose in the condition in which it emerged from the nitrator, i. e., without any of the usual neutralizing and purifying treatments, was satisfactory,

as shown by the German test results, as follows:

Minutes Salmon pink 45 Red fumes 45 Explosion 300 By reducing the temperature of nitration to an average of 50, the nitrogen content of nitroa Percent Nitric'acid' 67.7 Phosphoric acid 29.9 Water 2.4

-With such an arrangement, when the ratio of fresh acid to cellulose is maintained on the order of ten parts of acid to one part of cellulose or higher, the movement of the acid stream downwardly in leg 5 is sufiicient to carry along the water molecules released by any nitration which takes place in that leg, as the change in specific gravity of the acid after the nitration reaction is insufiicient to overcome the movement of the acid stream in the opposite direction. Accordingly, the composition of the acid which contacts the cellulose in leg 5 remains very nearly at the initial composition, with the highest nitrogen content, however, at the upper surface of the bath in leg 5.

From the foregoing description those skilled in the art should readily understand the operation and advantage'of the process and apparatus hereinbefore disclosed and realize that the invention accomplishes its objects. While one embodiment of the apparatus has been shown in the drawings and hereinbefore described, it is to be understood that the invention is not limited to the details of that showing, but that the same may be varied in accordance with the requirements of any given nitration, consistent with the principle that the nitrating tube be relatively long in the horizontal direction, with only sufficient central depression to maintain the tube substantially filled with nitrating acid, and yet permit the entrance and exit of the cellulosic sheet at an angle such that the natural sag of the sheetbetween points of suspension at the ends of the tube is reasonably approximated. Accordingly, the foregoing disclosure is to be regarded as illustrative and not limiting, save to the extent indicated in the appended claims. 1

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In the art of nitrating cellulose, the process comprising suspending a strip of cellulose at points substantially spaced horizontally so that the strip sags downwardly between the points of suspension and the freely suspended reaches of strip have substantial horizontal extent, and moving the freely, suspended reaches through a bath of nitrating acid, said bath being confined about the strip so that the top level of the bath of nitrating acidjimmediately above the valley of the strip is substantially below the top level of the bath where the stripv enters and leaves it.

2. The process of claim 1 wherein the acid is moved in a direction counter current to the movement of the strip. l

3. The process of claim 1 wherein the acid bath consists of nitric acid, phosphoric acid and water.

4. The process of claim 1 wherein each increment of strip is progressively advanced from the first point of suspension through the descending reach and then up the ascending reach to the second point of suspension.

5. The process of claim 4 wherein the N03 content of the acid bath is higher on the ascending reach than on the descending reach.

6. The process of claim 1 wherein the strip is rolled at the valley of the sag within the acid bath.

WILLIAM C. RAMSEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Number Number Name Date Mowbray Aug. 12, 1890 Cady June 4, 1918 Gross et a1 Feb. 23, 1932 Berl Sept. 4, 1945 Litkenhous Aug. 10, 1948 FOREIGN PATENTS Country Date Great Britain 1894 Great Britain 1899 Germany Aug. 19, 1920 France June 7, 1924 

1. IN THE ART OF NITRATING CELLULOSE, THE PROCESS COMPRISING SUSPENDING A STRIP OF CELLULOSE AT POINTS SUBSTANTIALLY SPACED HORIZONTALLY SO THAT THE STRIP SAGS DOWNWARDLY BETWEEN THE POINTS OF SUSPENSION AND THE FREELY SUSPENDED REACHES OF STRIP HAVE SUBSTANTIALLY HORIZONTAL EXTENT, AND MOVING THE FREELY SUSPENDED REACHES THROUGH A BATH OF NITRATING ACID, SAID BATH BEING CONFINED ABOUT THE STRIP SO THAT THE TOP LEVEL OF THE BATH OF NITRATING ACID IMMEDIATELY ABOVE THE VALLEY OF THE STRIP IS SUBSTANTIALLY BELOW THE TOP LEVEL OF THE BATH WHERE THE STRIP ENTERS AND LEAVES IT. 